1. Field of the Invention
The present invention relates to optical glass, and in particular, to optical glass having a relatively high refractive index and excellent devitrification resistance. The present invention also relates to an optical element using the optical glass described above as a raw material.
2. Description of the Related Art
In association with the recent spread and development of digital optical devices, there has been a demand for an optical lens of smaller size enabling higher performances. In order to meet this demand, use of an aspherical lens obtained through precision press molding is essential in optical design. Optical glass for use in such an aspherical lens as described above must have as high a refractive index (nd) as possible.
In response to these needs, optical glass containing Bi2O3 at a high concentration has been actively developed in recent years.
For example, as optical glass having a relatively high refractive index, Japanese Patent Application Laid-open No. 2006-327926 proposes optical glass containing Bi2O3 by 25 to 80 mol %, Japanese Patent Application Laid-open No. 2007-106625 proposes optical glass containing Bi2O3 by 10 mass % to 90 mass % (inclusive of 10 mass % and exclusive of 90 mass %), and Japanese Patent Application Laid-open No. 2007-099606 also proposes optical glass containing Bi2O3 by 10 mass % to 90 mass % (inclusive of 10 mass % and exclusive of 90 mass %).Further, Japanese Patent Application Laid-open No. 2002-201039 proposes a high refractive index glass for press molding, which substantially contains Bi2O3 at a concentration of 25 to 70% in mol % with respect to oxides.
However, none of the optical glasses disclosed in the aforementioned references has sufficient stability and moldability.